The invention pertains to process and an apparatus for continuously controlling the texture, in particular the crystallization, of material systems in the fluid state, in particular fat containing substances, such as chocolate masses. This is accomplished through a thermal treatment by cooling and counteractive heating wherein the cooling is done to such an extent that when the material system is in a state of rest it spontaneously solidifies, and that heating is done by means of energy dissipation through a mechanically adjustable energy supply resulting from shearing stress.
The contents of many food products include, among other raw materials, varying percentages of animal and/or vegetable oils and/or fats, or combinations of these (for example chocolate, butter and margarine), in crystallized form.
The final products owe their essential and characteristic properties to these crystallizable material systems.
Until now, crystallizable material systems have been frequently cooled in thermally controlled scraper heat exchangers or in double-walled containers (with jacket cooling, and an agitator equipped with scrapers), undergoing mechanical blending at temperatures below their freezing point, with variable efficiency in terms of speed. Most fats and fatty mixtures have the property of forming various polymorphic structures of their fatty crystals with different configurations of their fatty molecules (for example in the case of cocoa butter, .alpha., .gamma., .beta.', and .beta.-crystal modifications). The stability of these crystal modifications differs widely, and is responsible for the consistency, texture, surface luster (for example in chocolate) and mechanical properties of the final product (hard-soft, short-long structure, plastic/elastic-brittle, sticky-dry, gritty-smooth).
With the machines and types of apparatus that have been known up until now, temperature and duration control, as well as temperature gradients during cooling and reheating are only regulated on an empirical basis for different kinds of matter systems. Hence the particular fixed crystal modifications for the achievement of specific properties can only be obtained fortuitously.
One such apparatus is known, for example from DE-PS 39 13 941 and EP-OS 289 849.
As a measure of the blending intensity involved, shear gradients of from 500 to 4000 s.sup.-1 are produced. With regard to the square of the number of rotations and hence the shear gradient dependent dissipated mechanical energy, this means a maximum difference in conditions of up to a factor of 64. Deliberately introducing mechanical energy while the highly sensitive crystallization processes are reaching fruition is out of the question here.
In addition, the significance of the size of "shear gradients" is limited to laminar layer flows, which means that the quantification used here of a "blending vortex" cannot properly be described by means of data about the shear gradient.
In this context it has not previously been thought to use a targeted supply of dissipated mechanical energy as a "heat source" as well as a structure-inducing means of non-vorticized, genuine shear flow.
From the earlier, non-published DE-P-41 03 575.5 a procedure is known for cream or butter crystallization which produces a more easily spreadable final product. This procedure works by introducing mechanical energy into a so-called "shear gap crystallizer", consisting of an external cylinder and a concentric internal cylinder which is rotationally driven.
What this model presents is the introduction of a constant supply of mechanical energy, for uniform and homogeneous blending purposes. There is no notion of an energy-dissipation-controlled operating method using control of number of revolutions. As in other crystallization procedures of the traditional kind, the thermal regulation of the operation takes place solely through appropriate temperature adjustment by means of a heating or cooling agent.
The invention's central task is to produce a process and apparatus as designated at the outset, which make possible the achievement of crystal modifications according to desired specifications, and hence of particular desired properties in the final product, in such a way as to be reproducible.
This task is essentially performed by means of process and an apparatus designed to carry out this process which are hereinafter described.
In practical terms, the present invention calls for a shear crystallization, conducted at a low temperature; in other words crystallizable material systems are subjected to a mechanically induced low-temperature crystallization. Cooling takes place, as directed by the invention, at crystallization temperatures that are extremely low relative to the state of existing technology. Using "counter-control", by the application of heat with the help of the uniform and homogeneous introduction of mechanical energy, an astonishingly flawless product is achieved with predominantly stable crystalline forms and within a sharply reduced time-frame. Heating by means of the introduction of mechanical energy takes place immediately and without any mentionable delay for all practical purposes. This makes possible an appropriately sensitive control mechanism, measuring for instance the viscosity of the material system that is being processed.
In other words, the cooling of the material system that is to be crystallized takes place to such a massive extent, according to the invention, that the system would spontaneously solidify and harden under static conditions as a material system. Through the introduction of mechanical energy, which proceeds with uniform homogeneity because of the gap geometry that has been effected, energy is dissipated with regular uniformity in the material system. This leads to the heating of the material system, which counteracts the spontaneous crystallization which would otherwise result from the low cooling temperature. Simultaneously the shear flow, at the low temperature levels deliberately selected for this reason, has the particular effect of causing distinct orientation conditions to be initiated for macromolecular components, which thereafter adopt what are apparently preferred "positions" for the formation of crystalline structures. The shear induced alignment of molecular units, and likewise the simultaneous extreme supercooling that takes place on the contact wall of the container, bring about an extremely sharp acceleration of seed-crystal formation and crystal growth.
In contrast to the state of the art, the present invention achieves a homogeneous introduction of mechanical energy as a result of the characteristic feature of its construction, namely a constant shear gap distance over the entire stressed cross section. The effect of this is that at any point on the shear gap in which the substance that is to be crystallized is subjected to stress, the introduction of mechanical energy is in an exceptionally strict sense constant; in other words energy is dissipated regularly and simultaneously in the material system.
The rapid seed-crystal formation leads to a large number of seeds, hence prevents the formation of a small number of large-size crystals (this large-growth pattern means a gritty final product). Besides, the predominance of the formation of the desired stable or unstable crystal modifications while the material system is undergoing polymorphic crystallization can be regulated to fixed specifications, using the introduced shear-energy. The sharply accelerated crystallization kinetics generated by the invention's prescribed mechanism means that small "reaction volumes" (free crystallizer volume-capacity) can be produced, through which flow can continuously pass. Shorter crystallization times are required for specific, fixed material systems, also smaller heat-exchange surfaces and reaction containers, and less cooling energy and less electrical energy, because smaller vessels are being used. Material systems investigated by way of examples from the area of fats (namely cocoa butter) exhibit crystallization times which, relative to crystallization treatment of the traditional kind, are shorter by a factor of more than 100.
The regulating process is by no means a slow-moving operation, but with no difficulty it can occur with the requisite speed and sensitivity to ensure a regular and uniform product. According to the invention's prescribed mechanism, this is done by adjusting the setting of the rotor's revolutions. This adjustment, short-term and massive, can be set to any degree desired, making for an extremely brief manipulation of the energy conditions in the shear gap. Determining a specific introduction of mechanical energy depends on the product's retention-time in the gap, i.e. its gap geometry, as well as the product-volume flow and the number of revolutions of the shaft.
The term "shear flow" as used in this description, means a smooth flow in which the molecular components of the material system are moved and aligned in parallel "layers" relative to one another. This alignment produces projected positions for the system's material components (such as fatty molecules) in relation to each other, making it easier to "latch" into a crystal lattice. This substantially speeds up the crystallization kinetics.
Provided the apparatus is developed according to the invention's specifications, as stated herein, fullest benefit can be drawn from the introduction of mechanical energy as a standard regulating parameter for crystallization conditions. Depending on a specifically fixed starting level for viscosity, the apparatus is so to speak "viscosity-controlled", namely by means of modifications made to the introduction of mechanical energy, in other words the setting of the rotor's revolutions.
The container's wall is "strongly cooled", as per the invention's prescription. During this process the danger of "freezing up" is avoided, since the substance that is to be crystallized is only allowed to experience "low-temperature shock" on the contact surface. Hence it forms seed-crystals at a rapid rate; but these seed-crystals then generate a blend temperature in combination with the substance that has not come into contact with the wall, and this prevents a rapid re-solidification and re-hardening. The introduction of mechanical energy needs to be apportioned so as to ensure that an over-strong localized heat-up is avoided, in order to inhibit the desired stable crystals that have already formed from re-melting.
Compared to the well-known procedural method for obtaining the crystallization of a multiplicity of macromolecular material systems, the mechanism specified by this invention yields substantial time advantages (by up to a factor of 100), as well as considerable economic advantages, due to the reduction in capital investments which is brought about by the markedly reduced crystallizer volume-capacity.
In principle only one temperature adjustment zone (or temperature zone) is really necessary, namely cooling alone, as against the 2-3 zones (cooling and heating) required by the familiar mechanisms that have been in use to date. The pre-crystallized substance leaves the mechanism with a specifically fixed viscosity, and in a state directly susceptible to processing and finishing (no subsequent reheating is needed).
Hereinafter the invention is explained and elucidated in greater detail, with reference to the design, with the aid of a basic main sketch and accompanying examples by way of illustration.